Padma Multipurpose Bridge Project

116. There will be extensive tree plantation around and within the open space of bridge end facilities.This will have significant long-term positive impact. There will be a transition phase between the earlyand full growth stage of green belt area development where there will be prevalence of hot air duringdry weather. However in the long-run the area will be of improved landscape and green environmentthat will bring comfort and pleasing appearance in the locality and will attract tourists.7.2.3.5 Public Utility Crossings117. The future of public utility crossing over the bridge will not have any potential significant positiveand negative impacts during O/M stage except accidental risk, which is covered in next section.Services are accommodated inside the bridge cross section between the planes of the truss at thelevel of the lower truss chord. A 760mm diameter high pressure gas main will run parallel to the trackinside the truss. The high pressure gas main will be supported by brackets attached to the truss. Thegas main requires expansion joints wherever there are expansion joints in the bridge, every 900m. Atexpansion joints there will be an omega joint in the pipe where a flexible section of pipe, some 40m inlength, is free to extend by rising and falling vertically depending on whether the gas main isrespectively expanding or contracting. On each bridge module the gas line is fixed rigidly to the bridgeat the fixed pier. A walkway will be provided both for emergency evacuation of the train and also formaintaining the pipe line. To ensure safety the ends of the pipe line at the abutments will be equippedwith a Rapid Closing Ball Valve controlled by a Safety Sensor able to detect the effects of ship impact,earthquakes and pressure loss. The provision of a 400kV power line will be accommodated at thesame level on the opposite side of the railway, again with a walkway provided both for itsmaintenance and also for emergency train evacuation.7.3 Project Related Significant Risks7.3.1 Construction Stage118. The south bank is prone to heavy erosion. Last five years, there has been 700m bank erosion insouth bank. Bank erosion in north bank is minor. The length of the bridge was 5.58km during thefeasibility study and it is now 6.15 due to the bank erosion. Seventy percent of the service area insouth bank (right side) has been eroded and might continue to erode during the pre-constructionstage. There are possible risks of erosion during the construction stage as well. In addition, theconstruction yard in Mawa side will also have potential risk of erosion during construction stage.7.3.2 O/M Stage119. The following risks are expected during the O/M of the project:120. Accidental Spills: The bridge and approach road will be used for transport of Hazardous andToxic materials from Chittagong and Dhaka to southwest part and there will be potential chances forspills from these vehicles during accidents. Hence, to address the issue, a spill contingency plan oremergency plan needs to be prepared with a set of measures to be followed to minimize the potentialadverse effects of spill of harmful substances that may pollute the environmental resources such assoil and water during accidents.121. Leaks and Explosion: Padma Bridge will provide access to high pressure (1,135 psig) gasmainand thus inherent hazards of leaks, fire and explosion associated with gas handling poses a majorthreat to the users and the society at large. Various kinds of fires might cause, such as:(a) Jet fire: - Jet fire is associated with release of Natural gas and depends upon the diameter ofpipeline and the leak size. If the natural gas pipeline has a leak at a certain point in its pathand given that an ignition source is available, Jet fire may occur. Jet fire is usually notassociated with rupture of pipeline.(b) Flash Fire: - Flash fire occurs due to a sudden intense fire impact caused by ignition offlammable materials. It is characterized by high temperature, short duration, rapidly movingflame front, and considerable shock waves. Flash fire is usually more prominent with leak ofnatural gas rather than rupture.122. Explosion might cause due to traffic accidents on the bridge and sudden impact on the gasmain.This will be a cause of huge disaster in the bridge.123. Flooding: Major flooding may cause the closure of approach road and bridge (including railway).The emergency response plan should consider response/action and evacuation plan.7-33